There are a great many commercially available ground levelling machines, including such machines for use on farms. It would often not be economically justifiable for most farmers to own an industrial ground levelling machine such as a motor grader. Consequently, machines have been developed for towing behind agricultural tractors or mounting on other prime movers such as front end loaders.
In most circumstances, ground that has been levelled should be as free as possible of localised dips and rises. To this end ground levelling machines are designed so that the path of the blade in a horizontal direction remains as true as possible. A prime mover inevitably moves up and down as it traverses the ground and any implement mounted on the prime mover will move up and down with the prime mover. In fact, in the case of an implement that is hung out cantilever fashion over the front or back of a prime mover, such movement will be exaggerated. U.S. Pat. No. 4,809,449 discloses a levelling apparatus of this kind, designed to be mounted on the lift arms of a front end loader.
One way of reducing the movement of a blade carried by the implement is to suspend the blade on a frame that is supported on ground wheels at its rear end. The greater the distance between the wheel and the blade, the less will be the degree of up and down movement of the blade. U.S. Pat. No. 4,236,586 discloses a leveller with a blade assembly mounted on such a frame.
In a set up in which such a frame is not used, the implement is commonly mounted on the prime mover by a mounting arrangement actuated by one or more hydraulic rams. Often the rams are controlled manually by the driver of the prime mover. Nowadays, however, the rams can be controlled automatically, using laser level technology. Manual control is cheaper but less reliable than automatic control.
With the development of more powerful tractors has come the possibility of increasing the blade length of ground levelling machines and hence the width of the swath of earth cut by the blade in a single pass. For example, levelling machines with blades of over 10 meters in length are now commercially available. Laser level technology has also made the use of longer blades more practicable. However, the use of longer blades has some disadvantages. First, any levelling machine with such a long blade is likely to be too heavy to be hung from the front or back of a prime mover. This is particularly so since the blade must be very stiff and will therefore be heavy, if it is to remain straight in use. The apparatus shown in the aforementioned U.S. Pat. No. 4,809,449 would certainly be too heavy if it was provided with such a long blade. The commercially available levelling machines having such long blades and known to the applicant are of the type in which the blade is mounted on a wheeled supporting frame.
Second, the length of the blade is likely to cause difficulties in transporting the machine from one work place to another. One way of overcoming this problem is to provide a folding blade. One example of a long folding blade is shown in the aforementioned U.S. Pat. No. 4,236,586. However, the structure of a folding blade is inherently likely to be less rigid and straight, and more complex and expensive than a one piece blade.